Men who have recovered from coronavirus should abstain from sex in order to avoid passing the virus on via their semen, a new study suggests.

Patients in China who donated samples several days after virus symptoms had faded were found to show evidence of Covid-19.

The findings have left scientists worried that the deadly disease could be sexually transmitted, raising the prospect of health chiefs advising people to avoid having sex for a set time after the end of their symptoms.

One of the patients in the study, at Shangqui Municipal Hospital in Henan Province, tested positive for Covid-19 in his semen 16 days after coming down with the virus and three days after clinical recovery.

"Abstinence or condom use might be considered as preventative means for these patients," the study, published in the Journal of the American Medical Association, said.

The research team said Covid-19 could be seeded to the male reproductive tract, especially where there is local inflammation.

"Even if the virus cannot replicate in the male reproductive system it may persist, possibly resulting from the privileged immunity of testes," they said.

Other experts have pointed out that the study, comprising 38 patients, is relatively small, and that only six of these patients had tested positive for the virus in their semen. Until now, researchers had previously found only 27 viruses in human semen.

It is not known whether the presence of Covid-19 in the testes affects men's reproductive capability.

Professor Richard Sharpe, from the MRC Centre for Reproductive Health at the University of Edinburgh, said: "As the authors point out, this finding raises the possibility that Covid-19 might also be transmissible via semen – and thus via sexual contact – perhaps including during the recovery phase, which would have disease management implications.

"Whilst this is a small study, that leaves many important questions unanswered – how long after Covid-19 infection does detectable virus persist in semen in those with a semen-positive result?

"It suggests that obtaining answers to such questions should be an additional priority considering our global need to understand the dynamics of person-to-person transmission of Covid-19."

So far, the means of transmission focused on by scientists is via droplets coming out of infected people's noses and mouths and entering bodies of other people via their mouths, noses or eyes.

The majority of the public health guidance to suppress transmission has focused on keeping people apart – ideally at least two metres, according to the UK Government – and hand-washing.

Officials warn people not to have sex if they have symptoms of coronavirus, but only to avoid transmission via droplets.

Allan Pacey, a professor of andrology at the University of Sheffield, said: "This is an interesting paper that shows that RNA for the virus responsible for Covid-19 can be detected in the semen of a proportion – 15.8 per cent – of men with a confirmed infection.

"This opens up the possibility that one route of infection may be through sexual contact, although this was not confirmed in the paper."

The new research contradicts previous findings that did not detect Covid-19 in the semen of infected patients, and scientists agree that bigger and more detailed studies are now needed.

Dr James M. Hotaling, from the University of Utah, which has previously investigated the question, said last month: "If a disease like Covid-19 were sexually transmittable, that would have major implications for disease prevention and could have serious consequences for a man's long-term reproductive health."